1. Field of the Invention
The present invention relates to a method of effectively preventing polymer scale from sticking, and particularly to a method of preventing polymer scale from sticking in a polymerization vessel during the polymerization of monomers having an ethylenically double bond.
2. Description of the Prior Art
In processes of preparing polymers by polymerizing monomers in a polymerization vessel, known to arise is the problem that the polymer sticks on inner wall surface and so forth of the polymerization vessel in the form of scale. Once the scale of polymer stick on the inner wall surface and so forth of the polymerization vessel, much labor and time are required as a result to remove the scale of polymers. Disadvantages may also result such that the yield of polymers and the cooling capacity of the polymerization vessel are lowered, and the sticked scale of polymers may peel from the surfaces to mix into a product, and the quality of manufactured polymers are thereby made poor.
As methods of preventing polymer scale from sticking on the inner wall surface and so forth of a polymerization vessel, there have been hitherto proposed, for example, a method in which a polar compound, a dye, a pigment or the like is coated on the inner wall surface (Japanese Patent Publication (KOKOKU) Nos. 30343/1970 and 30835/1970), a method in which an aromatic amine compound is coated (Japanese Pre-examination Patent Publication (KOKAI) No. 50,887/1976), and a method in which a reaction product of a phenolic compound with an aromatic aldehyde is coated (Japanese Pre-examination Patent Publication (KOKAI) No. 54,317/1980).
These are effective in preventing polymer scale from sticking, when vinyl halide monomers such as vinyl chloride or monomer mixtures mainly comprised of said vinyl halide monomer are polymerized.
However, in instances in which the monomers to be polymerized comprise other monomers having an ethylenically double bond such as styrene, alpha-methylstyrene, acrylate and acrylonitrile, these monomers have so large a dissolving power against the coating formed by the above sticking-preventing methods that part or the whole of the coating may be dissolved away. Consequently, it becomes impossible to effectively prevent polymer scale from sticking on the inner wall surface and so forth of a polymerization vessel. This sticking of scale particularly tends to occur when the polymerization vessel is made of stainless steel.
Japanese Patent Publication (KOKOKU) No. 46,235/1978 describes a process of polymerizing a vinyl monomer, in which prior to polymerization the inner wall surface of a polymerization vessel has been previously
(I) coated with (a) an electron donor organic compound and/or (b) an electron acceptor organic compound, and the coated surface has been treated with at least one selected from (c) oxidizing agent, reducing agent, acid and base, or irradiated with light, or
(II) coated with a compound obtained by treating said (a) component and/or said (b) component with said (c) component or obtained by irradiating said (a) component and/or said (b) component with light. As an example, it discloses a coating solution prepared by dissolving Sudan Black B (i.e., C.I.Solvent Black 3) as the (a) component and Nigrosine (i.e. C.I.Acid black 2) as the component (b) in an organic solvent, and treating the solution thus obtained with ethylenediamine at 90.degree. C. In this process, it is essential to react the (a) component and/or (b) component with the (c) component. Although, according to this process, improvement can be obtained to some extent, the number of polymerization runs which can be repeated without formation of polymer scale is only about 30 or less.
As one of methods for improving the scale preventing effects in the polymerization of monomers having an ethylenically double bond, Japanese Patent Publication (KOKOKU) No. 30,681/1985 describes a method in which a condensate obtained by reacting an aromatic amine compound with an aromatic nitro compound at a temperature of from 100.degree. to 250.degree. C. in the presence of a condensation catalyst, is previously coated on the inner wall surfaces, etc. of a polymerization vessel prior to carrying out polymerization. Another method, Japanese Patent Publication (KOKOKU) No. 30,682/1985 describes a method in which an alkali metal salt or ammonium salt of a sulfonated product obtained by sulfonation of the condensate of an aromatic amine compound with an aromatic nitro compound, is previously coated on the inner wall surfaces, etc. of a polymerization vessel prior to carrying out polymerization. According to these methods, scale formation on the inner wall surfaces, etc. of the polymerization can be fairly effectively prevented, so that about 20 to 80 polymerization runs can be repeated with little formation of polymer scale. However, more strong scale preventing effect is required so that productivity may be improved.